Premiere Features?

Wow...it's been a while since I've been here, but I remembered the way and I didn't even stop for directions...

I'm considering purchasing a Premiere, and have a couple of questions:

Am I right in thinking that the only differences between the 3 models are number of tuners, hard disk size, and THX cert. (I guess besides the remotes)? Are there any other differences in features between the 3?

How have the Premieres been as far as reliability...any problems to watch out for?

I have a couple of Series 3's now...one with cable cards and one without...used to back-up some recordings. I am thinking of going with a 4-tuner premiere and keeping one of the Series 3's active on cable. If I can swap out the 2 single-stream cards for 2 multi-stream cards, it shouldn't cost me any more per month.